electronics lecture2 3 diodeapp - mohaisendepartment of electrical, electronics and communications...

Korea University of Technology & Education

Department of Electrical, Electronics and Communications Engineering

Department of EECE

Diode Applications

Electronic Circuits

Dr. Manar Mohaisen Office: F208

Email: [email protected]



₪ Doping ■ It is a controlled addition of impurities to the pure semiconductive

material to increase its conductivity. ►The impurities addition is for target to increase either the holes or the

free electrons.

Review of the Precedent Lecture

Free (conduction) electronfrom Sb atom

SbSi

Si

Si

SiBSi

Si

Si

Si

Hole from B atom

n-type semiconductor. The extra electron from the antimony atom

becomes a free electron. The impurity element is a pentavalent. Impurities: Arsenic (As), antimony (Sb)

p-type semiconductor An extra hole is created because the impurity

element is a trivalent (i.e., it has 3 valence electrons)

Impurities: Boron (B), indium (In), gallium (Ga)



₪ Diode Approximations

Review of the Precedent Lecture – contd.

VR

IR

VF

IF

0.7 VVR

IR

VF

IF

0.7 VVR

IR

VF

IF

Reverse Current = 0

Ideal Diode Model -Reverse current, barrier potential, and dynamic resistance are neglected. Not accurate model. - Useful for troubleshooting to check whether the diode is working properly or not. - Forward current is given by:

BIASF

LIMIT

VI R=

Practical Diode Model -Reverse current and dynamic resistance are neglected. -Forward current is given by:

Complete Diode Model - Nothing is neglected. - The most accurate model. - Forward current is given by

After VBIAS exceeds the barrier potential, the diode

acts like a short circuit

VB = 0.7V Reverse

Current ≠ 0

BBIASF

LIMIT

V VI R−

= BBIASF '

LIMIT d

V VIR r

−=

+



₪ Explain the Operation of the Half-wave Rectifier

₪ Explain the Operation of the Full-wave Rectifier

₪ Discussions

₪ Explain the Use of Power Supply Filters and Regulators

₪ Explain Diode Limiting and Clamping Circuits

₪ Explain the Operation of the Voltage Multipliers

₪ Discussions

Class Objectives



₪ DC Power Supply

Introduction

can be half-wave or full-wave rectifier

smoothing filter (Low-pass filter)



₪ Connection 1 ■ Forward Bias

► In the first half cycle, the diode is forward-biased.

► If the diode is ideal, the output voltage equals the input voltage.

■ Reverse Bias ► In the second half cycle, the

diode is reverse-biased.

►There is no output (Vout = 0).

₪ Connection 2 ■ Reverse biasing in the first

half period

■ Forward bias in the second half period.

Half-Wave Rectifier

RL

+ –

+

–

Vout

0 tt 00 tt 11

Vin

0 t t22

I

RL

Vout

tt 00 tt 11

Vin

00

+–

I = 0 A–

+t t22

Connection 1

Connection 2

RL

+–

+

– Vout

0tt 00 tt 11

Vin

0 t t22

I



₪ Average Value

₪ Peak Inverse Voltage ■ Equivalent to the peak value of the input voltage.

►Diode should be capable of withstanding this repetitive reverse voltage.

Half-Wave Rectifier – contd.

0/2

0/2

0

1 ( )

1 2sin( ) ,

cos( )1

2cos cos(0)22

TAVG

Tp

Tp

p p

V x t dtTV t dtT T

V tT

TTV V

TT

πω ω

ωω

π

ππ

⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦

⎡ ⎤⎛ ⎞⎢ ⎥⎜ ⎟⎜ ⎟⎢ ⎥⎝ ⎠⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎣ ⎦

=

= =

−=

− += =

∫

∫



₪ Example 2-2

■ Ideal Diode ►The peak output voltage = Vp(in) = 5 V and 100 V, respectively.

►VAVG = Vout / π = 1.59 V and 31.83 V

■ Practical Diode ►The peak output voltage = Vp(in) – 0.7 = 4.3 V and 99.3 V,

respectively.

►Find the average output voltage in this case [Homework: +2points].

Half-Wave Rectifier – contd.



₪ Center-Tapped Full-Wave Rectifier

Full-Wave Rectifier

RL

D2

D1F

Vin

+

–

+ –

– +

+

–

–+

0

Vout

0

I

RL

D2

D1F

Vin

+

–

– +

+ –

–

+

+–

0

Vout

0

I

During the first half cycle, the upper diode is forward-biased and the lower diode is reverse-biased.

During the second half cycle, the lower diode is forward- biased and the upper diode is reverse-biased.



₪ Turn Ratio ■ The ratio between the number of turns in the secondary winding

and those in the primary winding. Designated n.

■ Affects the output voltage.

■ Peak Inverse Voltage

Full-Wave Rectifier – contd.

(sec) (sec)(sec)

( )

PIV 0.7V 0.7V2 2

2 0.7 V

p pp

p out

V VV

V

⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

= − − − = −

= +



₪ Example 2-5


(sec) ( ) 0.5(100 V) 50 Vp p priV nV= = =

(sec)( ) 0.7 24.3V2

pp out

VV = − =

( )PIV 2 0.7 2(24.3) 0.7 49.3Vp outV= + = + =

Is this figure correct?



₪ The Bridge Full-Wave Rectifier ■ Uses four diodes connected as

shown.


+

–

+

–

F

Vin

D3

D4

D1

D2RL Vout

+

–0

I

–

+

–

+

F

Vin

D3

D4

D1

D2RL Vout

+

–0

I

( ) (sec) 1.4Vp out pV V= −

(sec)

( )

PIV 0.7V0.7V

p

p out

VV

= −

= +



₪ The Bridge Full-Wave Rectifier ■ Vp(sec) = 12 V rms

■ Input is sinusoidal, then

■ Root Mean Square


(sec) (sec)( )2 17 Vp p rmsV V= =

( ) (sec) 1.4 17 1.4 15.6Vp out pV V= − = − =

( )PIV 0.7 15.6 0.7 16.3 Vp outV= + = + =

2 22

0 0

2

0 0

2

1 1sin( ) cos(2 )2 2

1 cos(2 )2 2

2 2

T Tp p

rms

T Tp

p p

V VV t dt t dtT T

V dt t dtT

V VTT

ω ω

ω

⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦

⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦

= = −

= −

= =

∫ ∫

∫ ∫





₪ Discussions




₪ Discussions

Class Objectives



₪ Objective ■ Convert the AC power line voltage into a DC voltage.

■ The fluctuation in the filter output voltage is called ripple.

₪ Capacitor-Input Filter ■ Consists of a capacitor connected from the output of the rectifier

to the ground.

Power Supply Filters and Regulators

Vin

0 V Filter 0

VOUTFull-waverectif ier

Rectified output

RL

+

–

Vin+

–VC



₪ Capacitor-Input Filter – contd. ■ Positive 1st quarter cycle:

►Diode is forward-biased.

►Capacitor charges to within 0.7V of the input voltage.

►Load and capacitor have the same voltage.

■ Remaining part of the cycle ►Diode is reverse-biased.

►Capacitor discharges in the load at a rate determined by RC.

■ 1st quarter of next cycle ►Diode becomes

forward-biased.

Power Supply Filters and Regulators – contd.



₪ Capacitor-Input Filter – contd. ■ Ripple voltage

►The variation in the capacitor voltage due to charging and discharging

►The smaller the ripple, the better the filtering performance.

■ Ripple factor ► It is an indication of the effectiveness of the filter.

► It is defined as


( )

DC

r ppVr V=

without filter

DC voltage of the filter’s output voltage

( ) ( )1

r pp p rectL

V Vf R C⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠

≅

DC ( )11 2 p rect

LV Vf R C

⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠

= −



₪ Capacitor-Input Filter – contd. ■ Half-wave vs. Full-wave rectifiers




₪ Example 2-7 ■ Vp(pri) = 1.414 Vrms = 1.414(120 V) = 170 V

■ Vp(sec) = n Vp(pri) = 0.1(170 V) = 17 V

■ Vp(rect) = Vp(sec) – 1.4 V = 17.0 V – 1.4 V = 15.6 V

■

■

■


( ) ( )1 1 15.6V 0.591V(120Hz)(220 )(1000 F)r pp p rectL

V Vf R C μ⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠=≅ =Ω

DC ( )1 11 1 15.6V 15.3V2 2(120Hz)(220 )(1000 F)p rect

LV Vf R C μ

⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠= − = − =Ω

( )

DC

0.591V 0.03915.3Vr ppV

r V= = =



₪ Surge Current in the Capacitor-Input Filter ■ Before closing the switch, the capacitor is uncharged

►Uncharged capacitor acts as a short circuit.

■ When the switch is closed ►An initial current, called surge current, passes through the diodes D1

and D2.

■ To avoid defecting the diodes, a fuse is used. ►A fuse is a protection device.

►A slow-blow fuse is generally used.

►Slow-blow indicates a slow melting of the wire inside the fuse.


Fuse (source: wikipedia.org]



₪ Voltage Regulators ■ A regulator is connected to the output of the capacitor-input filter.

■ It maintains a constant output despite changes in the input.

■ The input of the regulator should have a ripple < 10%.

■ Percent Regulation

►Line regulation .

►Load regulation , where NL and FL refer to no load

and full load (i.e., maximum load)


F1

D2

D3 D1

T1

D4+ +

VoltageregulatorSW1

C2C1

Output capacitor To improve the transient response

Capacitor-input filter

OUT

IN100%V

V⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

Δ= Δ

NL FL

FL100%V V

V⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

−=



₪ Diode Limiter (Clipper)

■ Clips either positive or negative part

₪ Example 2-9 ■ R1 = 10 kΩ

■ RL = 100 kΩ

■ Vp(in) = 10V

Diode Limiting and Clamping Circuits

( ) ( )1

Lp out p in

L

RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

= +

( ) ( )1

100k 10V 9.09V110k

Lp out p in

L

RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

= +

Ω= =Ω



₪ Biased Limiters ■ A limiter that has a bias voltage in series with the diode.

■ The diode is forward-biased when Vp(in) exceeds the voltage bias by 0.7 V (i.e., Vp(in) = 0.7 + VBIAS). ►Since the load is connected in parallel with the diode and bias voltage

● V(out) = VBIAS +0.7 V.

■ Otherwise, the diode is reverse-biased. ►The peak output voltage is then given by:

Diode Limiting and Clamping Circuits – contd.

Vin

RL

R1

0+

–

VBIAS + 0.7 V

VBIAS

0

( ) ( )1

Lp out p in

L

RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

= +

Positive limiter



₪ Biased Limiters – contd.


What is the input at this point?



₪ Biased Limiters – contd. ■ Example 2-10

■ When VA exceeds 5.7 V ►D1 becomes forward-biased.

►V(out) equals 5.7 V.

►D2 is still reverse-biased.

■ When VA goes below -5.7V ►D2 becomes forward-biased.

►V(out) equals -5.7 V.

►D1 is still reverse-biased

■ For values between 5.7V and -5.7V ►Both diodes are reverse-biased.

►Depending on the load value, the input voltage is partitioned between R1 and the load.




₪ Voltage-Divider Bias

■ VBIAS is simply given by


VBIAS is the voltage applied to R3

3BIAS SUPPLY

3 2

RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠

= +



₪ Example 2-11


Vin

RL

R1

0+

–

VBIAS + 0.7 V

VBIAS

0

3BIAS SUPPLY

3 2

220 12 8.25 V220 100RV VR R

⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠

= =+= +

8.25 V

= 8.95 V

Note that there is a power supply of 12V and R2

parallel to the bias voltage. These two elements are not shown in the figure.



₪ Diode Clampers ■ A clamper is a circuit that adds a DC level to an AC signal.

►Clampers are also referred to as DC restorers.

■ The capacitor charges and acts as a DC voltage source. ►RC time constant should be large enough to avoid discharging of the

capacitor. RC = 100 for excellent clamping action.




₪ Diode Clampers ■ Example 2-12

►When the input reaches about +0.7V, the diode is forward-biased.

►The capacitor is charged up to (-(24V – 0.7) = -23.3 V)

● Consider the polarity of the capacitor!

►The diode is then reverse-biased.

►The capacitor acts as a DC voltage source (consider a negligible discharging)

►The circuit can be analyzed as if it includes an AC voltage source and a DC voltage source (The later one replaces the capacitor).




₪ Voltage Doubler ■ Half-wave Doubler

►During the positive half cycle

● D1 is forward-biased, and C1 is charged to Vp less the diode drop.

● D2 is reverse-biased.

►During the negative half cycle

● D2 is forward-biased and C2 is charged by both the input and C1 which acts as a DC voltage source. C2 is charged to (2Vp –1.4 V )

● D1 is reverse-biased.

►The output is a half-wave filtered voltage.

Voltage Multipliers



₪ Voltage Doubler ■ Full-wave Doubler

►Class discussion

● Groups of students analyze the full-wave doubler based on the following Figures.

Voltage Multipliers

0

Vp

C1

–

++

–Vp

C2

Reverse-biased

D2

D1

0–Vp

+

–+

–

2Vp

Reverse-biased

D2

D1

+

–

+

–Vp

+

–

Vp

I

I+

–

C1

C2



₪ Voltage Tripler ■ 1st positive half cycle

►D1 is forward-biased.

►C1 charges to Vp – 0.7 V.

■ 1st negative half cycle ►D2 is forward-biased.

►C1 acts as a DC voltage source.

►C2 charges to 2(Vp – 0.7).

■ 2nd positive half cycle ►D3 is forward-biased.

►C1 and C2 acts as DC voltage sources.

►C3 charges to 2(Vp – 0.7).

Voltage Tripler & Quadrupler

Voltage Tripler

Voltage Quadrupler





₪ Discussions




₪ Discussions

Summary and Discussion



Discussion & Notes

AK

K

K

AK

A

A

K

A

K A

K

A

K

AK

K

A

K

K

A

electronics lecture2 3 diodeapp - mohaisendepartment of electrical, electronics and communications...

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